1. Field of the Invention
The present invention relates to a brain function examination by the utilization of a pupillary light reflex. More specifically, the present invention relates to a brain function examining apparatus and a method therefor, wherein the pupillary light reflex exhibited by a subject is detected to determine a cerebral disorder such as, for example, the degree of senescence of the brain, disorder of the autonomic nervous system, the dementia or the like.
2. Description of the Prior Art
It is generally said that the size of a pupil decreases with age (for example, Ishikawa, et al., xe2x80x9cFukyuu-gata Denshi Doukoukei Irisukohda (C-2514) ni Tsuite (On Handy Electronic Pupil Meter Iriscorder (C-2514))xe2x80x9d, (Shinkei Ganka (Neuro-Ophthalmology), Vol. 10, No. 2, pp. 106-110, 1993). The smooth muscle that adjusts the size of the pupil is governed by the autonomic nervous system and the size of the pupil and/or the pupillary change reflect the degree of activity of the autonomic nervous system.
It is also pointed out that the pupil is associated with the Alzheimer""s disease which is generally considered closely associated with the brain function. L. F. M. Scinto, et al. have reported that by measuring the rate of dilation of the pupil before and after a dilating agent is instillated, diagnosis of the Alzheimer""s disease which is considered one of dementia is possible (xe2x80x9cA Potential Noninvasive Neurobiclogical Test for Alzheimer""s Diseasexe2x80x9d, Science, 266, pp. 1051-1054, 1994). According to this method (hereinafter referred to as an instillation method), since diagnosis of the Alzheimer""s disease is done in reference to the rate of dilation of the pupil, the result of such diagnosis is subjective. In this respect, it may be said that the instillation method is more excellent than the interview-based medical examination which tends to result in subjective results. Determination based on the interview-based medical examination includes, for example, The Revised version of Hasegawa Dementia Scale (HDSR) which has hitherto been used in diagnosing dementia. By the way, measurement of the pupil based on the installation method requires 30 minutes and cannot be applied to some of subjects suffering from ophthalmic diseases.
To overcome the above discussed inconveniences, a diagnosis technique is available in which the characteristic of the pupil (the pupillary light reflex) is measured to determine if dementia is apparent. This is based on researchers"" report that the normal and dementia cases exhibit different pupillary light reflexes (Shi, et al., xe2x80x9cA Study for Objective Measurement of the Senile Dementia by Light-Reflexxe2x80x9d, lyou Densi to Seitai Kougaku (Medical Electronics and Bio-engineering), Vol. 36, No. 3, pp. 210-214, 1998). According to this diagnosing method, unlike the installation method, measurement of the pupillary light reflex completes in a short time and has an advantage that the measurement brings no side-effect.
However, according to the Fumi, et al. report, the normal and dementia cases are merely compared with each other by calculating predetermined indexes (pupillary constricting rate, pupillary constricting time and pupillary redilating rate) indicative of the pupillary light reflex. Accordingly, it is not possible to output (display), for example, a subject index and an average index for the dementia cases and then to utilize a relative relationship displayed in determining if the subject is suffering from dementia or the like. Also, since the pupillary light reflex varies from person to person as is the case with physiological indexes, it cannot be said that with only the three indexes reported by Fumi, et al. the manner of pupillary change is sufficiently grasped. Accordingly, determination of the dementia, the degree of autonomic activity, the degree of senescence of the brain function or the like with the use of such small indexes lacks reliability.
On the other hand, it is not wise to increase the number of the indexes representative of the pupillary light reflex. While increase of the indexes will result in increase of the accuracy of diagnosis, the fact that many indexes must be taken into consideration will make it difficult to achieve a targeted determination. Also, in view of any possible adverse influence strongly brought about by the particular indexes, it may occur that obviously contradictory results of determination will occur. In such case, it may be very difficult to employ which one or ones of results of determination of what index.
The present invention provides a brain function examining apparatus for performing an examination of a brain function by detection of a pupillary size of a subject, which apparatus comprises: a light source for illuminating a pupil of the subject; a pupillary detector for detecting the pupillary size; an index calculating unit for calculating a subject index indicative of a characteristic of the pupil based on the pupillary size detected by the pupillary detector; a database for storing a base index indicative of a characteristic of a pupil that can be used as a reference; an output unit for outputting the subject index, calculated by the index calculating unit, and the base index stored in the database.
For example, the characteristic of the pupil is a quality associated with variation of the pupillary size and wherein the subject index calculated by the index calculating unit includes at least one of a natural size of the pupil, latency, pupillary redilating time, the amplitude of pupillary constriction, pupil constricting rate, pupil constricting velocity, maximum velocity of pupillary constriction, pupil redilating velocity, maximum velocity of pupillary redilation, pupillary constricting acceleration, maximum acceleration of pupillary constriction, time required to attain the maximum velocity of pupillary constriction, time required to attain the maximum velocity of pupillary redilation, and time required to attain the maximum acceleration of pupillary constriction.
For example, examination of the brain function is that of dementia, and/or examination of the brain function is that of a degree of brain senescence.
Preferably, the brain function examining apparatus further comprises a determining unit for comparing the subject index, calculated by the index calculating unit, with the base index stored in the database to determine a condition of the subject""s brain function.
Preferably, the output unit also outputs a result of determination performed by the determining unit.
Preferably, the brain function examining apparatus further comprises a multivalue calculator for calculating discriminant scores based on a plurality of input values, the number of said calculating discriminant scores being smaller than that of the input values; wherein the index calculating unit calculates a plurality of subject indexes and the database stores a plurality of base indexes; and wherein the multivalue calculator calculates subject discriminant scores using the subject indexes, calculated by the index calculating unit, and the base indexes stored in the database, as the input values.
Preferably, the multivalue calculator calculates base discriminant scores using the base indexes as the input values, and further comprising a determining unit for comparing the subject discriminant scores, calculated by the multivalue calculator, and the base discriminant scores to determine a condition of the subject""s brain function.
Preferably, the output unit outputs at least one of the subject discriminant scores calculated by the multivalue calculator, the base discriminant scores and a result of determination performed by the determining unit.
Preferably, the database stores as the base index, the index indicative of the characteristic of the pupil of one of a normal case, an autonomic disorder case, a dementia case and an Alzheimer-type dementia case.
Preferably, the determining unit performs determination of one of a degree of senescence, autonomic activity, dementia and Alzheimer""s disease of the subject.
For example, the light source emits a step light to the pupil, a flash light to the pupil. Preferably, the light source emits the flash light to the pupil for a duration shorter than a pupillary response latency and/or the light source emits a bundle of light of a size smaller than a minimum possible pupillary size.
Preferably, the pupillary detector detects a time-based change of the pupillary size of the subject and wherein the index calculator is operable to determine a time-based change of an average pupillary size by calculating a mean of a plurality of time-based changes of the pupillary size detected by the pupillary detector and to calculate the subject index based on the average pupillary size.
Preferably, the pupillary detector detects a time-based change of the pupillary size and wherein the index calculator is operable to determine a time-based change of an average pupillary size by moving-averaging a plurality of time-based changes of the pupillary size detected by the pupillary detector and to calculate the subject index based on the average pupillary size.
Preferably, the determining unit is operable to compare some of the subject indexes with some of the base indexes corresponding thereto and to determine, based on a result of comparison, one of progressive senescence of the subject""s brain function and probability of the subject suffering from brain disorder.
Preferably, such some of the subject indexes and such some of the base indexes includes at least two of a natural size of the pupil, latency, pupillary redilating rate, pupil constricting velocity, maximum velocity of pupillary constriction, pupil redilating velocity, maximum velocity of pupillary redilation, pupillary constricting acceleration, and maximum acceleration of pupillary constriction.
Preferably, the determining unit determines one of progressive senescence of the subject""s brain function and probability of the subject suffering from brain disorder in the event that at least one of situations in which the natural pupil size of the subject is small, in which the latency is large, in which the pupil constricting velocity is low, in which the maximum velocity of pupillary constriction is low, in which the pupil redilating velocity is low and in which the maximum velocity of pupillary redilation is low establishes.
The present invention provides a method of examining a brain function of a subject by detecting a pupillary size of a pupil of the subject, which method comprises the steps of: illuminating the pupil with light; detecting the pupillary size; calculating a subject index indicative of a characteristic of the pupil based on the pupillary size; storing a base index indicative of a characteristic of a pupil that can be used as a reference; and outputting the subject index calculated and the base index stored.
For example, the characteristic of the pupil is a quality associated with variation of the pupillary size and wherein the subject index calculated by the index calculating unit includes at least one of a natural size of the pupil, latency, pupillary redilating time, the amplitude of pupillary constriction, pupil constricting velocity, pupil constricting rate, maximum velocity of pupillary constriction, pupil redilating velocity, maximum velocity of pupillary redilation, pupillary constricting acceleration, maximum acceleration of pupillary constriction, time required to attain the maximum velocity of pupillary constriction, time required to attain the maximum velocity of pupillary redilation, and time required to attain the maximum acceleration of pupillary constriction.
Preferably, the method of examining the brain function as claimed in claim 21, further comprising a step of performing a multivalue calculation based on a plurality of input values, the number of said calculating discriminant scores being smaller than that of the input values; wherein the calculating step is a step of calculating a plurality of subject indexes, the storing step is a step of storing a plurality of base indexes, and the calculating step is a step of calculating subject discriminant scores using the subject indexes, calculated by the index calculating unit, and the base indexes stored in the database, as the input values.
Preferably, the calculating step is a step of calculating base discriminant scores using the base indexes as the input values, and further comprising a step of comparing the subject discriminant scores calculated and the base discriminant scores to determine a condition of the subject""s brain function.
Preferably, the storing step is a step of storing as the base index, the index indicative of the characteristic of the pupil of one of a normal case, an autonomic disorder case, a dementia case and an Alzheimer-type dementia case.
Preferably, the determining step is a step of determining one of a degree of senescence, autonomic activity, dementia and Alzheimer""s disease of the subject.